In order to improve efficiency (system total throughput and transmission rate) of communication in the communication system, adaptive modulation schemes have been studied to determine a modulation scheme, channel coding rate, error correcting coding scheme, spreading factor, the number of code multiplexes, transmit power, a combination thereof or the like (hereinafter, referred to as a modulation parameter) corresponding to a reception state (see Non-patent Documents 1 and 2).
In the communication system adopting the adaptive modulation scheme, it is necessary to notify a communicating party apparatus of propagation path conditions as described below or a modulation parameter selected corresponding to the propagation path conditions as information obtained from the reception state. The propagation path conditions include:
“SNR: Signal to Noise power Ratio”;
“SIR: Signal to Interference power Ratio”;
“SINR: Signal to Interference plus Noise power Ratio”;
“CNR: Carrier to Noise power Ratio”;
“CIR: Carrier to Interference power Ratio”;
“CINR: Carrier to Interference plus Noise power Ratio”;
“DUR: Desired signal to Undesired signal power Ratio”;
“Ratio of average reception energy per symbol to noise power density (Es/No)”;
“Ratio of average reception energy per bit to noise power density (Eb/No)”;
“Ratio of average reception energy per symbol to interference power density (Es/Io);” and
“Ratio of average reception energy per bit to interference power density (Eb/Io)”.
For example, in a system comprised of a base station apparatus and terminal apparatuses adopting Frequency Division Duplex (hereinafter, abbreviated as “FDD”) in communications (hereinafter, referred to as downlink) from the base station apparatus to terminal apparatuses and communications (hereinafter, referred to as uplink) from the terminal apparatuses to base station apparatus, when the adaptive modulation scheme is applied on downlink, it is possible to configure systems as described below.
(1) The terminal apparatus estimates propagation path conditions from a reception signal on downlink, and notifies the base station apparatus of the estimated propagation path conditions as the uplink notification information. The base station apparatus selects a modulation parameter for data to the terminal apparatus on downlink based on the notification information to perform adaptive modulation, and prior to transmission of the data subjected to adaptive modulation, notifies the terminal apparatus of the selected modulation parameter as the downlink notification information.
(2) The terminal apparatus estimates propagation path conditions from a reception signal on downlink, selects a modulation parameter for transmission data to the terminal apparatus on downlink based on the propagation path conditions, and notifies the base station apparatus of the selected modulation parameter as the uplink notification information. The base station apparatus performs adaptive modulation on the data to the terminal apparatus on downlink based on the modulation parameter, and prior to transmission of the data subjected to adaptive modulation, notifies the terminal apparatus of the selected modulation parameter as the downlink notification information.
In addition, in the description of the invention, notification information that is simply described indicates either or both of the uplink notification information and the downlink notification information.
Such a system has been proposed that CIR obtained from a latest downlink reception signal is compared with the total sum of previous notification information, and that binary information indicating a decrease or increase is notified as the uplink notification information (see Non-patent Document 3).
FIG. 53 is a block diagram showing an example of a configuration of a notification information generating apparatus 900 that generates conventional notification information.
A determining section 901 receives a CIR measurement value measured from a reception signal, and outputs the CIR measurement value as notification information without modification in initial notification, while outputting the CIR measurement value to an accumulator 902. Further, the determining section 901 receives a storage value stored in the accumulator 902, compares the CIR measurement value with the storage value except the initial notification, and outputs notification information of “UP” when the CIR measurement value is larger, while outputting a value (addition result) obtained by adding 0.5 dB to the storage value to the accumulator 902, outputs notification information of “DOWN” when the CIR measurement value is smaller, while outputting a value (addition result) obtained by adding −0.5 dB to the storage value to the accumulator 902, or outputs the CIR measurement value when the CIR measurement value is equal to the storage value.
The accumulator 902 stores the CIR measurement value or the addition result input from the determining section 901, and outputs the stored storage value to the determining section 901.
For example, in a multicarrier communication system for transmitting information using a plurality of subcarriers, such a subcarrier adaptive modulation scheme has been studied that adaptive modulation is performed for each subcarrier or for each block comprised of a plurality of subcarriers to further improve efficiency of communication (see Non-patent Documents 4 and 5).
In such a subcarrier adaptive modulation scheme in the multicarrier communication system, it is necessary to notify a communicating party apparatus of information obtained from the reception state on a subcarrier basis or on a subcarrier block basis.
In the multicarrier communication system, such a scheme has further been proposed that for CSI (Channel State Information) that is information obtained from the reception state, a plurality of subcarriers is grouped, new CSI is obtained by subtracting an average value of CSI of the group from original CSI, the group is further divided into a plurality of subgroups, the average value is calculated similarly for each subgroup and subtracted from original CSI, such operation is repeated in subgroups of a plurality of hierarchies, and that an average value obtained in each hierarchy is updated in a different period for each hierarchy and notified (see Non-patent Document 6).
Further, in the case of performing adaptive modulation in a system of Orthogonal Frequency Division Multiplexing Access (hereinafter, abbreviated as OFDMA) that is a multiple access system originated from Orthogonal Frequency Division Multiplexing (hereinafter, abbreviated as OFDM) that is one of multicarrier communication systems, such a scheme has been proposed that for a selected band (group of subcarriers), CQI (Channel Quality Indicator) that is uplink notification information is notified using a difference value from the last notification (see Non-patent Document 7).    Non-patent Document 1: “A Study on Adaptive Modulated High Mobility OFDM Radio Transmission System”, Takako Yamamura et al. Technical report of IEICE RCS99-146, November, 1999, p. 33-40    Non-patent Document 2: “Experimental Evaluations of Adaptive Modulation and Channel Coding in Forward Link for VSF-OFCDM Broadband Wireless Access”, Yoshihisa Kishiyama et al. Technical report of IEICE RCS2003-25, May, 2003, p. 7-14    Non-patent Document 3: “Medium Access Control (MAC) Standard for cdma2000 Spread Spectrum Systems Release D”, ARIB STD-T64-C.S0003-D v1.0, Association of Radio Industries and Businesses, September, 2005, p. 2-145-2-147    Non-patent Document 4: “OFDM Based Adaptive Modulation Systems with a Multilevel Transmit Power Control for High Bit Rate Transmission”, Tomoaki Yoshiki et al. The transactions of the Institute of Electronics, Information and Communication Engineers, B Vol. J84-B, No. 7, July, 2001,    Non-patent Document 5: “On OFDM/TDD Transmission Scheme with Subcarrier Adaptive Modulation”, Fumiaki Maehara et al. Proceedings of the IEICE General Conference, B-5-100, March, 2001, P. 498    Non-patent Document 6: “A Study on CSI Feedback Bandwidth Reduction Method for FDD-based OFDM Systems”, Katsuyuki Motoyoshi, Proceedings of the Society Conference of IEICE, B-5-28, September, 2005, p. 428    Non-patent Document 7: “Uplink CQI channel for OFDMA PHY”, IEEE802.16d-04/84rl, (US), IEEE, Apr. 28, 2004